Synthesis of Methylene-Bridge Polyarenes through Palladium-Catalyzed Activation
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[12] In a crowded environment, the C H bond in a methyl
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À
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procedure is not so efficient as they described. We re-
peated the coupling reaction of 1,2-dibromobenzene
with 2-tolylboronic acid three times and fluorene (3a)
was indeed observed in ca. 50% GC yield. 2-Methylbi-
À
[7] For reviews of aryl C H bond activation, see: a) E. M.
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À
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phenyl (15–20%) and 1,2-bisACTHNUTRGNEUGN(2-tolyl)benzene (15–30%)
were obtained as the serious by-products. Replacing
1,2-dibromobenzene with 1-bromo-2-chlorobenzene or
changing ligand PCy3 to PCy3·HBF4 could not improve
unsatisfactory results. Our optimal condition is also in-
efficient for this tandem reaction.
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3
À
C
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[9] Several protocols involving metal-catalyzed functionali-
[16] Compound 4 and its steroisomer were obtained as an
inseparable mixture after the chromatography. Crystal-
lization from CH2Cl2/MeOH gave pure fluorene 4. Un-
fortunately, the accurate structure of the stereoisomer
of 4 cannot be assigned based on 1H- and 13C NMR
and mass spectra.
À
zation of the benzylic C H bond with the subsequent
À
C C bond formation have been reported. Pd: a) T. Ke-
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(sp3)-H
activation, see: M. Lafrance, S. I. Gorelsky, K. Fagnou,
J. Am. Chem. Soc. 2007, 129, 14570.
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should be more acidic than those in 1a and 1c, see:
a) F. G. Bordwell, D. Algrim, N. R. Vanier, J. Org.
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[19] The formation of benzocyclobutenes through the C-
3
À
G
montet, R. Piccardi, N. Audic, J. Hitce, J.-L. Peglion, N.
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